There are situations in which it is necessary to obtain an assessment of the degree of astigmatism of a cornea of an eye. For example, when a surgeon has made an incision in the cornea as part of an operating procedure such as insertion of an intraocular lens, it is necessary at the end of the procedure to close the incision by means of sutures. However, the sutures have to have an appropriate degree of tension to avoid inducing excessive stigmatism in the cornea. The lens of the present invention enables the surgeon to monitor readily the degree of astigmatism in a cornea as suturing is in progress and to adjust the tension of the sutures if necessary.
For example, closure of the surgical wound following cataract extraction and intraocular lens implantation may result in significant postoperative astigmatism. The amount of astigmatism is often unpredictable and may be a major factor limiting visual recovery and the final result of the procedure.
As surgical techniques and lens design have improved, other more serious complications have reduced in frequency. Patients' expectations have also increased and an excellent visual result following surgery is considered one in which patients not only have good corrected acuity, but are also able to see well without spectacles. The major problem which prevents ophthalmic surgeons from obtaining such a result is often the presence of surgically induced astigmatism. The introduction of multifocal and bifocal implants is another factor suggesting that levels of astigmatism previously considered routine may no longer be acceptable. At a recent conference (EIIC 1988) in Copenhagen, a panel of experts uniformly agreed that surgically induced astigmatism was the major remaining problem with their surgery over which they had inadequate control. This is one of the reasons why phacoemulsification and small incision cataract surgery is being considered by an increasing number of surgeons.
Even with these advanced techniques, astigmatism can still be a problem if wound closure and suture tension is not carefully monitored. Surgical Keratometers have been introduced to enable surgeons to monitor the corneal astigmatism during wound closure and adjust suture tension accordingly. These instruments have varied from complex and expensive instruments such as the Terry Keratometer to simple metal or plastic devices such as the Karickoff device which reflect a circle of light on the cornea. All these devices operate in a similar principle in that the reflected image of a circular light source will have an elliptical shape if significant astigmatism is present. More expensive instruments use incandescent or fibreoptic light sources to provide a bright image whilst the cheaper qualitative keratometers use reflected light from a metal or plastic circle. Unfortunately, the brightness of the corneal image with the qualitative keratometers is inadequate and the reflection is difficult to recognise. These qualitative keratoscopes have to be held at just the right angle to produce an image which is often difficult to recognise. The more expensive Keratometers produce adequate images, but are complex and time consuming. This has restricted their use to a small number of surgeons. The lens of the present invention is relatively inexpensive to produce compared to known qualitative Keratoscopes whilst providing a relatively bright reflected corneal image compared to known qualitative Keratoscopes.